There will be all sorts of plugins that will do that, but a fairly easy way in PS7 is to make the background image into a layer, lower the opacity in "layer style-blending options", then flatten the image again. There are lots of other ways of getting equivalent results, and you might try the emboss or notepaper filter -among other possibilities- to simplify the image before lightening it.

Or you could just play with the brightness/contrast sliders, which is probably the quickest way.